If Clifford becomes the QB one of the 2019 QBs are gone after the season and the 2020 is looking elsewhere.
Clifford will have three years to play regardless. The 2019 kids will have two years left after Clifford is gone and the 2020 kid will have three. I'm not sure why you think who wins the job this fall has any impact on any of the three kids. One 2019 kid may transfer because of how he looks vs. the other 2019 kid, not how he stacks up next to Clifford.